Slipform pavers are generally well-known and are produced and widely distributed, for example, by the applicant and assignee of this patent application. Slipform pavers are not only used to slipform fresh concrete but also used to place other granular materials described above.
Road building machines typically do not carry their own concrete or materials to pave. Rather, apparatuses such as material placers are used for receiving trucks hauling the materials to be delivered in bulk then, metering this material to the material placer on board belt(s) which in turn transfers the material and controls the delivery rate to something or someplace else. In the case of a road building machine, the material placer distributes the materials over an area that will be paved or onto a road paver hopper, and then the road paver building machine forms this material into long strips. This paved material is often used in the context of projects for forming the base and concrete on highways, airport runways, and the like. In this manner, the pavers are continuously supplied with fresh material as they travel in the direction of the strip. The road building machines form the freshly supplied material into a rectangular, cross-sectional shape, and then properly pre-compacts or compacts and finishes the top surface of the strip. Other road construction related machines, such as barrier wall forming machines or asphalt base laying machines, can also be fed with such material placers. Materials that are placed by such machines can include, but are not limited to, concrete, gravel, sand, asphalt, bitumen, slurries of various composition, and the like.
Accordingly, the placing of material can be a bottleneck point, where the road building process is limited by factors including: (i) the rate at which the material can be provided to the material placer, (ii) the rate at which material can be loaded onto the material placer, and onto its transfer conveyor, via a hopper, and (iii) downtime of the material placer which is caused by hardening of concrete or asphalt on hard-to-access parts of the material placer (e.g. a conveyor belt).
Approaches that have attempted to improve the throughput of material placer hoppers have included the use of drag chains, extra augers, hydraulic folding hopper walls, and the like to transfer materials from the hopper to the conveyor. Other approaches include static physical extensions to a hopper, providing extra rollers or augers, and using supplementary feed hoppers to receive concrete or other materials before delivering to a primary hopper. These extra devices have been added to traditional hoppers in an attempt to have the largest practical holding capacity in the material hopper so a truck hauling material can quickly dump its load and pull away to allow the next truck to cycle. Minimizing the time necessary to dump the material load helps to achieve shorter discharge times and higher production, while still being able to move the last bit of material from the truck bed to the auger located at the back of the hopper, which in turn carries the material to the conveyor. Such approaches have been less than ideal, introducing extra equipment, failure points, moving parts, additional costs for training, maintenance, and machinery, and further complexity to concrete placing projects.
Further as noted, problems with concrete being fed through material placers is well known in the industry including downtime resulting from the accumulation of hardened concrete on parts of the equipment. For example, hardened concrete can build up on the tail pulley of the transfer conveyor, increasing its diameter then breaking a conveyor belt or freezing up rollers supporting the conveyor belt. While routine cleaning and maintenance should in theory avoid persistent breakdowns of this nature, in practice, the difficulty for an operator or laborer to reach the areas requiring cleaning located in the interior of the machine on a daily or even hourly basis results in a calculated negligence and tolerance for delays when the machine does inevitably break.
Another limitation of material placers known to the industry is that, when used on a jobsite, they are generally designed with fixed ground clearance underneath them. More specifically, with a fixed clearance between the ground and the tail pulley of the two conveyors. Only the material receiving hopper is designed to raise and lower by a limited amount, with the tail end of conveyor transferring material out of the hopper by raising and lowering with the hopper. Much like an automobile traveling on uneven or rutted ground or transitioning too quickly from flat to slope, material placers known to the industry experience the same problems, such as parts of the material placer interfering with the ground or other obstructions. The only way to overcome this limitation on an automobile or material placer is to have a higher ground clearance, or the ability to increase the ground clearance when uneven ground is encountered or when there is a need to move from a flat to a steep surface.
Examples of material placers known in the industry that exhibit aspects of the above noted problems and design deficiencies can be found, for example, in: U.S. Pat. App. Pub. No. 2006/0239806, U.S. Pat. App. Pub. No. 2009/0242316, U.S. Pat. App. Pub. No. 2008/0173736, and U.S. Pat. App. Pub. No. 2008/0175666, each of which are herein incorporated by reference.
Such operational limitations of placing concrete and other materials, and the corresponding limitation in construction throughput, affects the entire road building process because it slows down the material laying speed that can be attained for a project. This is highly undesirable because delays in the timeline of a project significantly increases overall material laying costs.